1. Technical Field
The invention relates to a projection screen and method. More particularly, but not exclusively, it relates to a projection screen retained by a retention member, and a method for constructing such a screen.
2. Description of the Related Art
The projection of an image upon a partially reflective and partially transparent screen such that it is observable by a viewer positioned in front of the screen is known as a “Pepper's ghost” arrangement from fairground shows.
Pepper's ghost projections have been used in publicity and promotional displays where a presenter resides behind an inclined, partially reflective partially transparent screen, typically a tensioned foil, onto which an image of, for example, a motor vehicle is projected, via at least one reflective surface, see for example EP 0799436. The location of the presenter behind the projected image has a number of inherent advantages over systems where the presenter stands in front of a screen, not least of which is that the presenter does not obscure the projected image when walking across the projected image. Additionally, the use of an inclined screen results in a viewer of the image perceiving the image as having depth rather than merely being a two dimensional image, for example where a motor vehicle is seen to rotate upon a turntable.
However, current image projection apparatus' do have a number of problems associated with them, for example, mounting of the foil can prove difficult which in turn leads to uneven tensioning of the foil and wrinkles upon the foil, that impair the viewed quality of the image. It is well known in the art that wrinkles inevitably form in a screen over a period of time with a resultant distortion of the projected image. Indeed, a wrinkle-free screen may be assembled in the evening, and by the following morning, wrinkles will have appeared as a result of the screen settling. Furthermore a change in conditions, such as humidity or temperature, can cause wrinkles to form in the space of minutes. In practice, it has been found that due to the thickness of large sized foils (e.g. 4 metre length foils are 88-110 microns thick and 5.5 metre length foils are approximately 50 microns thick) settling of the screen often only occurs after approximately 48 hours. When wrinkles appear, it is necessary to retension the screen and in particular the levels of tension required exceed those achievable by user force alone.
WO 2005/096095 (Musion Systems Limited) provides an apparatus capable of providing even tensioning of the foil by application of pressure at a plurality of positions along at least one edge of the screen. This apparatus requires placing an edge of the screen between jaws and passing a bolt through the screen. A nut is then threaded onto the bolt and tightened to hold the screen between the jaws. Tensioning is provided via straps which are attached to the jaws. Each of the tensioning straps can be tightened or loosened individually to allow an even tension to be applied over the whole of the screen.
There is becoming an ever increasing need for Pepper's ghost projections in more unusual locations and similarly a great need for larger projection images requiring larger screen sizes (such as those in excess of 5 metres in length). This is placing an increasing burden on the complexity of construction of a projection apparatus capable of projecting a high quality image.